The subject matter disclosed herein relates generally to magnetic actuators, and, more particularly, to magnetic actuator configurations including more than one air gap.
Devices such as circuit breakers, accessories for circuit breakers, and relays, for example, include a trip unit that, when a predetermined level of current is sensed, opens the current path to stop the flow of the current through an electrical circuit. Circuit breakers are well-known and commonly used to provide this automatic circuit interruption when undesired overcurrent conditions occur. Overcurrent conditions can include, but are not limited to, overload conditions, ground faults, and short-circuit conditions. The ability to break the flow of current is usually achieved by having a movable contact(s), which is attached to a movable arm or blade, that separates from a stationary contact(s), which is attached to a stationary arm or blade. The trip unit includes a magnetic actuator, which is the component that drives the tripping action using, in general, a spring-biased mechanism to force the movable blade, and therefore the movable contact, away from the stationary contact.
In general, the magnetic actuator component of the trip unit is designed to react as quick as possible, yet magnetic actuators with one air gap, however, start slowly due to their initial mass and large initial airgap and therefore generate low forces during the initial portion of the travel. Attempts have been made to improve the reaction time, but these improvements have come with unwanted costs. For example, a higher number of turns of a trip coil winding would increase the force acting on the magnetic actuator allowing for a faster reaction time, but with the higher number of turns of the coil winding comes an unwanted and unacceptable increase of power loss from the circuit breaker, thereby causing inefficiency and an increase in overall size.
It would, therefore, be desirable to have magnetic actuators that provide improved reaction times, but without the drawbacks that comes along with known magnetic actuators.